Color demodulator



Feb. 16, 1960 D. H. PRITCHARD :Er 11u.

COLOR DEMODULATOR 2 Sheets-Sheet l Filed Jan. 28, 1955 Pam/.f a

as? i AD. H. PRlTcHARD ETAL Feb. 16, 1960 COLOR DEMDULATOR 2 Sheets-Sheet 2 Filed Jan. 28, 1955 3 frequency less than 0.6 mcs. is accurately reproduced over the entire area enclosed by the triangle 11 in Figure 1. B. Color detail, which produces significant signals of frequency greater than 0.6 mcs. and less than,l.5 mcs. is reproduced in hues which lie along the orange-cyan axis 15 or 17, depending upon the type of color image reproducer utilized.V l*

C. Color detail which produces signals' `of frequency i greater than 1.5, mcs. is reproduced in,monochrome Vat the point representing illuminant C bearing the designator 13 in Figure 1.

The preceding tabulation may be generalized as follows: in regions of reduced detail, three-color information .Gloystein and Turner in their article entitled, ,The Colorplexer-a Device for Multiplexing Color Television Sgnals in Accordance with the NTSC Specifications, as published in the January 1954 issue of the Proceedings of the I.R.E., the subcarrier, which hasa frequency of 3.58 mcs., is modulated to provide the chrominance'signal which may be described by the vector diagram shown in Figure 2. In this vector diagram which describes the continuous change of hue which is containedv in the chrominance signal, the phase angle yields theindication of hue, while the sub-carrier amplitude, when considered along with the corresponding lluminance level, gives an indication of saturation. White or neutral colors fall at the center of the diagram since these produce no subcarrier components. Any given color or color diiference information signal, then corresponds to an axis or line on this vector diagram.

Since the chrominance signal is susceptible to demodulation by the processes of synchronous demodulation, a color synchronizing burst is included on the back porch of each horizontal synchronizing pulse; vthe colorv synchronizing bursts convey the reference phase information corresponding to the burst phase shown in Figure. 2.

It is seen in Figure 2 that the I and -I signals 21 which describe the orange and cyan color difference information respectively are disposed in phase whereby therphase of the I signal lags the burst phase by 57. The Q and -Q signals 23 which describe the purple and green color difference information respectively are dis- -posed in phase whereby the phase of the Q signal lags the I signal by 90. The phase of the R Y; color differ-l ence information signal 22 is seen to'lag the burst phase lby 90. A synchronous detector devised'to explore a prescribed phase shown in vFigure 2 will'also-explore the phase, 180 out of phase with lrespect to that prescribed phase-though yielding the corresponding color. diiference signal in reversed polarity;,it` will be realized therefore that further reference in the specification to color difference information signals of the I, iQ A:and (R-Y) variety is unnecessary in that it isunderstood hereinafter that reference to aQ signal or to an R--Y color difference information signal, for example, also implies the demodulation of -Q and ''(RY) color difference signal by the synchronous demodulator ofthese signals.V Y

' lAccording to the 'present invention, Vthere is one gamut of color difference information signals, to be described in detail, which will yield color television image reproduction wherein the higher frequency color information in the range from substantially 0.6 to 1.5 rncs. is fully and accurately reproduced. By selecting the Q signal and one or more color difference information signals from this gamut for forming the component color information signals containing the aforementioned high frequency color infomation, rather than by restricting the selection to only I and Q signals, simplification of circuit design and improvement in circuit perfomance as derived from the nature and characteristics of the color difference information signals chosen may be realized. For example, lwhen `Q and R-Y color difference information signals are utilized, the following is'true: (a) In color hold circuits of the type which utilize, for example, phase discriminators forY frequency control in conjunction with a reactance tube of a local oscillator for producing the reference subcarrier, the phase of the color oscillator can be optimally causedto fall in synchronism at a phase removed frornthat of the color `synchronizing burst. This phase corresponds to `the R-Y color difference information signal phase. If the R-Y color difference information signal is one of the pair of color difference information signals utilized for the production of cornponent color signals describing the color television image, 'it then follows that at least one of the phases of the required synchronous demodulating signals lis therefore automatically developed. (b) The recovery of the R-Y, B-Y and G-Y color difference signals from any pair 'of demodulated color .difference information signals depends largely upon the accuracy and vmaintenance of tolerances of Veach of the associated circuits` which are utilized for matrixing the demodulated color difference information signals. in magnitude due to heating'or prolonged use, or should the replacementof a tubeprovide into the circuit a new tube of slightly different characteristics, then the color difference information signal provided by the matrixing Yofthe demodulated color diiference information signals mayVV constitute aconsiderable departureV from the desired R-Y, B-Y and G-Y color4 diiference information signals in both the low frequency and higher frequency color difference information signal ranges. If, for example, one of the demodulated color difference information signals is one of the three desired color difference information signals'required for the reconstruction of the color image, say the Rv-Y color difference information signal, it follows'then that this one of the three desired color diierence information signals will always be accurately produced in a manner relatively independent of circuit parameters; in addition, the matrixlng of one `accurately produced color difference information signal with a second color diiference information signal may be utilized to'produce others of thethree desired color difference vinforrrnation signals with improved accuracy. (c) If one of the dernodulated color difference information signals is, for example, chosen to be 'the R-Y color difference information signal, the accuracy of waveform of this color difference information signal may be easily checked by adding a suflicientamount of luminance signal to the R'Y color diierenceinforma'- tion signal to provide the recovery of a component red information signal which may be then compared with the red content Vin anV appropriate region of the color lmage.

Numerous experiments by the present inventors have shown that if either the I or Q signals is to be'utilized w1th a second color difference information signal for matrixing to provide recovery of high definition cornponent color information signals, the Q signal com"- ponent is the more desirable component for providing orange-cyan axis information in thehigher frequency color range. When the Q signaly component was chosen as one of the two demodulated color difference information signals it was found that one ofl a very large gamut of color difference information signals in' a 'phase range from the vicinity of the burst phase to a phase between the R--Y and Q phases could be utilized as Should a circuit parameter change applied `to the loud speaker '4 9,

Semaployed in the colorl television' Ireceiver toffurnish'the component blue information signal/tothe .color image repodcr 'must' rbe,I vof 'considerably' highrxgain'Y `than tlilse channels,` which; forv example; furnish thecOrn= `811') pr'inty green informationsignals.V It then' rfollowszthat if other than blue information ndsflits Way intvthe blue channel due to the inability oflfa matri'x'-to provide accurate color information at .the higher'fcolor frequencies, this improper and" spurious col'r infrmationewill bfe amplified yto a highlevel' and reproduced-by the color image reproducen :Figure 3 is a which lt'nperates followingthe teachings of the .p'resen't invention.' One ofthe.twol.den'xodulatedv color signals employed is the Q signal; The second colorgdiierence information signal is the R-Y color difference informa.- tion signal. i e f I.

The incoming color television signal arrivesat` the antenna 41 and is'V applied to the television signal amplie'r 43. In the television signalre'ceiver. 43 numerous functions are provided, namely rst detection',.intermedi' ate frequency arnplication;` second detectionr andauto-v matic gain control. The operation of the television signal receiver has been described in detail;- for example, Vby Antony Wright `in his Varticle entitled, Television ,Receivers, published in the RCA vReview .for March` 1947.l It is to be understoodI that the operation, ofa television signal receiver does not constitute;aiparticulariunction ofthe present invention that its'gfunction isgonlyt'o demodulatefand provide a recovered 'color television signal which may thenbeemployed in the luminance, l

ehrfominance yand *..synchronizingV channels `.in A`a whichgonforms -to the teachings ofthe prsetiriventin. U'iliZillg tl darrierfsound, 4the vsovund information is"'recover'.ed `f thevcolor `television signal, detectedfi'th'e'jadio euratefhig erfrequency fork example, the v'velly known principles 'of detienen;

diagram of V'a' colontelevisioif. receiver 1 ursts fromthe c or "'tel' then applied f frm-n the.v colori oscillatorfotojthfe phasesynchronizing bursts, aeval'sa generated. The gatepulses 6Z`are then appliedto theburst separaton to'which the reciovered col'o television. signal 'iisalsogapplied The burst separatgr :63.C01isists of, a gaten Y i' Ttiegce'lerteljeyisien sigan is: applied y to; the enigmi- Y Qfaemedjtitater '77.' The .iena ...iS ,analisti i0 ef 'that ililimn sider thelop'eration o .PhS- Synchronous deio 1` control, grid. 129j thej sa .lfbe .nl `SYIIIIO-F nosfdemodlation of `the1Q"`sigralfis` 'thereby furnisV i inzth Q' den'iddulair?? with. this Q Signal iilt'ered in' 1111's Q lter 79. `The` .Q .lter 7-9f'consi'sts.fof'fthellovvY p'as's filter 133 liaviriaiciruit' constanis..whih,pr'vid a naiss baiidffrom 0`to` 0.6`lm1c`. and a modegoffrcoupling which ctul'ples the iilt'er-Q' signal to the' control grid"140'o`f the electrontube 139. The electron .tube `1,39; ris theon'trol device of the; Q amplifier and inverterl., having' ifut- 'putnplate resistor 1 37 and anY output cathode-resistor 141 'thereby providing a +Q`signalfto the output terminal 83 and: a -Q signal to the output terminal 85.Y The. phase Shift` Circuiti? isyadiusted iQ provide an RLY phase Synchronous demodiilatiiigsi'gnali iheldiifput irminlzl' from which; terminali;islappliedio th 'detecter 45, athplined fnth'e audio amplin'e'rmfane j '.Tlj'e recovered color televisionjsignal Vis titilizedfprin- VVcvipally nfour branches to .provide .th'efsig'nals rvwhich niay be .employed .for reconstruction of the. televisedcolor image by the lcolor imagereproducer 57, Y i

One xbranch A provides tlierecoveredV color television signal in'the'form o'f 'the 'luminance signal'through the Y is bien c'ctupledA .t0 'the icbntrolerid. 170' of., the elect second eeatmigrid 15a-orme eleet'ren tubensl. irhgje chrominance signal is coupled fromy vtheApotexitiornef'.17'75 to'thejcontrolfgrid 15.5- Synhr0nouadnidu1atib` fimcs. and also to havephasevdelayjvvhich delay line 51 wherefrom vit is" applied to thefYk-amplier .Y Y'

` 5, '1f-he amplified luminnce'signal is Athenprovided at terminal J54 andv simultaneouslypplied to the .resistor Irfnatriceysr95, 97 and 119;]v 'Y g v e v QThe r'recovered color-televisionlsignl isalsbfpplied" ifet'heieaetion and high voltage-'erfenis 61 Vwhich@sea- .5

Signal; the -AR"..Y: color diierence; information :signal the luminance-signalarevaddedgttggether R-i/:R-Y (1) B-Y=2.44 Q-1.17 (rz-Y) (2) Gar/:n.455 Q-.295 (rz-Y) (3) By performing the process of matrixing according to the Equations 2 and 3 in the matrices V97 and 95 respectively, in conjunction with proper amounts of luminance signal, bl'ue and green component color signals are provided to the blue and green amplifiers 103 and 101 respectively.

The outputs of these amplifiers are then used to 'drive' the color image reproducer 57.

The use of the R--Y color difference information signal in conjunction with the Q signal in the circuit shown in Figure 3 has the advantage that the R-Y color difference information signal is one of the color difference information signals which is utilized for final recovery of the televised color image. In addition, since esh tone and orange-cyan edge effects are highly dependent upon the R--Y color diierence information,it`is to the advantage of the color television receiver design that the R-Y color difference information signal be provided immediately 'by one of the pair of color diiference signal demodulators. i

While the use of the R-Y and the Q colo-r difference information signals for image reconstructiomhas the obvious advantage already `described in these specifications, in other forms of the invention, a variety of auxiliary color difference information signals utilized in conjunction with the Q signal may be employed for obtaining optimum edge color reproduction lying in the range between the I signal and the burst phase. It is to be understood, of course, that each choice of color difference` information signal pairs entails the design of a specific matrix which will provide both vlow frequency color difference information signals and reproduction'of the edge color reproduction along substantially the orange-cyan axis.

Having described the invention, what is claimed is:

1. In a color television receiver, the combination of, a. source of a chrominance signal including a Q signal and au R-Y color difference information signal in a first frequency range and orange-cyan axis information in at least a second frequency range, said Q signal and said R-Y color difference information signal having phases in said chrominance signal lagging a reference phase by 147 and 90, respectively, a circuitto provide intermittent color synchronizing bursts each having a phase related to said reference phase, means coupled to said burst providing circuit to develop a first oscillatory signal having a phase corresponding to the phase of said Q signal in said chrominance signal and a vsecond oscillatory signal having a vphase corresponding to the phase at the phase Vof said R`Y color kdifference information signal from said chrominance signal, said rsecond tcolor difference information signal'` having a 'frequency'vfband which includes'both said first frequency range and said second frequency range, circuitl means for combiningjse- `lected magnitudes and polarities of each of vs'aidQx signal and 'said second color difference information signal' to develop color diffe-rence information signals corresponding to red, green and blue color difference information signals in said first frequency range andVorange-cyan 'axis information in said second frequency range.

2. In a vcolor television receiver, the combination of, a source of color television-signals representing a color image and including ya luminance signal, and a chrominance signal which includes information describing a gamut of color difference signals including a-wide bandwidth I signal describing orange-cyan axis information and a narrow bandwidth Q signal which describes greenpurple axis information, said I and Q signals included in said chrominance signal at phases lagging a reference phase by 57 and `147, respectively, said color television signal also including color synchronizing bursts having said reference phase, means to separate said color synchronizing bursts-from said color television signals, means coupled to said burst separator means and responsive to said separated burstsA to develop an oscillation which is synchronized to a phase prescribed by said separated bursts, means coupled to said source and operatively connected to be responsive to a iirst phase of said oscillation developed by said oscillation developing means for demodulating said Q signal, means coupledto `said source and operatively connected to be responsive to a second phase of said oscillations provided by-said oscillation developing means for demodulating -a second color difference signal at other than a phase lagging the reference phase by 57 and containing at least a prescribed portion of orange-cyan axis information, means for combining selectedmagnitudes and polarities of said Q signal and said second color difference information signal to form a prescribed trio of color difference signals which also describe the orange-cyan axis information over t-he wide bandwidth of said I signal.

3. In a color television receiver, the combination of, a source of color 4television signals representing a color image and including a luminance signal and a chrominance signal including signal information describing a gamut of color dierence signals including an R-Y color difference information signal and a Q signal in a first frequency range, and orange-cyan axis. information in a second frequency range, said R-Y color difference information signal and said Q signal in said first frequency range having phases lagging a reference phase by and 147, respectively, said color television signal also including color synchronizing bursts having said reference phase, means to separate said color synchronizng bursts from said color television signal, means coupled to said burst separator means and responsive to said separated bursts to develop an oscillation having a phase synchronized by said separated bursts to a phase related to said reference phase, means to develop from said oscillation a first demodulating signal having a phase corresponding to said Q signal in said chrominance signal, means -to develop from said oscillation a second demodulating signal having a phase corresponding to said R-Y signal in said chrorninance signal, means coupled to said source and to said rst demodulating signal developing. means for demodulating said Q signal, means coupled to said source and to said second demodulating signal developing means for demodulating an ReY color difference signal which also includes higher frequencyY components in said second frequencyrange which describe orange-cyan axis information, circuit means for combining selected amplitudes and polarities of said Q signal and said R-Y color difference information signal to form a prescribed trio of color difference signals which also describe color information along an orange-cyan axis in said second frequency range.

References Cited in the file of this patent UNITED STATES PATENTS 2,713,607 Rhodes Iuly 19, 1955 2,725,422 Stark et al. Nov. 29; 1955 2,732,425. Pritchard Ian. 24, 1.956 2,840,634 Bedford June 24, '1958 

